Identification, characterisation and clinical applications of cosmids from the telomeric and centromeric regions of the long arm of chromosome 22

Cosmid-derived transcripts and sequence tags mapped to three subregions of human chromosome 22

Fifty cosmids from the ICRF, London, and Lawrence Livermore Laboratory, California, human chromosome 22 cosmid libraries were isolated, regionally assigned and tested for their ability to detect repeats or single copy sequences. The search resulted in nine cosmids containing repetitive motifs from the pericentric region of chromosome 22. An additional 19 cosmids, that detected single copy sequences in the long arm of chromosome 22q: 7 in the region 22q11.2-q13.1 and 12 in 22q13.1-qter, were mapped more precisely by fluorescence in situ hybridization. Three out of these 19 recombinants displayed restriction fragments containing (CA)n repeats, were subcloned and sequenced. One cosmid, representing a region coding for an ubiquitous 300-bp transcript, is localized 600 kb from PDGFB, and four cosmids contained sequences surrounding the ARSA gene at 22q13.3. Presently, long range physical maps, that may be useful for analysing structural alterations of chromosome 22q13, are being constructed from these additional, regionally assigned markers from chromosome 22q13 employing both existing cosmid and new bacterial artificial chromosome (BAC) libraries.

Partial disomy of Xp and the presence of SRY in a phenotypic female

We present a study of a mentally retarded and mildly dysmorphic female in whom initial cytogenetic studies identified the karyotype 46,X, + mar. Further characterisation of the structurally abnormal chromosome by fluorescence in situ hybridisation (FISH) showed that it is composed of both X and Y chromosome material with a centromere originating from the Y chromosome. The presence of the DMD gene and the absence of the XIST gene was shown by FISH using locus specific probes. The Y segment included the SRY and ZFY genes. Based on these findings, the karyotype was defined as 46, X,der(Y)t(X;Y) (p21.1;q11). This case illustrates male to female sex reversal owing to a partial duplication of the short arm of the X chromosome in the presence of SRY.

Fifty probands with extra structurally abnormal chromosomes characterized by fluorescence in situ hybridization

Extra structurally abnormal chromosomes (ESACs) are small supernumerary chromosomes often associated with developmental abnormalities and malformations. We present 50 probands with ESACs characterized by fluorescence in situ hybridization using centromere-specific probes and chromosome-specific libraries. ESAC-specific libraries were constructed by flow sorting and subsequent amplification by DOP-PCR. Using such ESAC-specific libraries we were able to outline the chromosome regions involved. Twenty-three of the 50 ESACs were inverted duplications of chromosome 15 [inv dup(15)], including patients with normal phenotypes and others with similar clinical symptoms. These 2 groups differed in size and shape of the inv dup(15). Patients with a large inv dup(15), which included the Prader-Willi region, had a high risk of abnormality, whereas patients with a small inv dup(15), not including the Prader-Willi region, were normal. ESACs derived from chromosomes 13 or 21 appeared to have a low risk of abnormality, while one out of 3 patients with an ESAC derived from chromosome 14 had discrete symptoms. One out of 3 patients with an ESAC derived from chromosome 22 had severe anomalies, corresponding to some of the manifestations of the cat eye syndrome. Small extra ring chromosomes of autosomal origin and ESACs identified as i(12p) or i(18p) were all associated with a high risk of abnormality.